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doc-rst: dmabuf: Add ioctl cross references 

There are lots of ioctls mentioned there that aren't cross-referenced.

Convert the const to cross references. That makes it visually
better, and improves navigation along the document.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Mauro Carvalho Chehab 2016-07-04 16:43:03 -03:00
parent 8f764eb97c
commit 69eee8a512
1 changed files with 22 additions and 19 deletions
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41
Documentation/linux_tv/media/v4l/dmabuf.rst
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@ -20,9 +20,9 @@ exporting V4L2 buffers as DMABUF file descriptors.
Input and output devices support the streaming I/O method when the
``V4L2_CAP_STREAMING`` flag in the ``capabilities`` field of struct
:ref:`v4l2_capability <v4l2-capability>` returned by the
:ref:`VIDIOC_QUERYCAP` ioctl is set. Whether
:ref:`VIDIOC_QUERYCAP <VIDIOC_QUERYCAP>` ioctl is set. Whether
importing DMA buffers through DMABUF file descriptors is supported is
determined by calling the :ref:`VIDIOC_REQBUFS`
determined by calling the :ref:`VIDIOC_REQBUFS <VIDIOC_REQBUFS>`
ioctl with the memory type set to ``V4L2_MEMORY_DMABUF``.
This I/O method is dedicated to sharing DMA buffers between different
@ -34,7 +34,7 @@ such file descriptor are exchanged. The descriptors and meta-information
are passed in struct :ref:`v4l2_buffer <v4l2-buffer>` (or in struct
:ref:`v4l2_plane <v4l2-plane>` in the multi-planar API case). The
driver must be switched into DMABUF I/O mode by calling the
:ref:`VIDIOC_REQBUFS` with the desired buffer type.
:ref:`VIDIOC_REQBUFS <VIDIOC_REQBUFS>` with the desired buffer type.
.. code-block:: c
@ -57,10 +57,10 @@ driver must be switched into DMABUF I/O mode by calling the
}
The buffer (plane) file descriptor is passed on the fly with the
:ref:`VIDIOC_QBUF` ioctl. In case of multiplanar
:ref:`VIDIOC_QBUF <VIDIOC_QBUF>` ioctl. In case of multiplanar
buffers, every plane can be associated with a different DMABUF
descriptor. Although buffers are commonly cycled, applications can pass
a different DMABUF descriptor at each ``VIDIOC_QBUF`` call.
a different DMABUF descriptor at each :ref:`VIDIOC_QBUF <VIDIOC_QBUF>` call.
.. code-block:: c
@ -119,7 +119,7 @@ Captured or displayed buffers are dequeued with the
buffer at any time between the completion of the DMA and this ioctl. The
memory is also unlocked when
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` is called,
:ref:`VIDIOC_REQBUFS`, or when the device is closed.
:ref:`VIDIOC_REQBUFS <VIDIOC_REQBUFS>`, or when the device is closed.
For capturing applications it is customary to enqueue a number of empty
buffers, to start capturing and enter the read loop. Here the
@ -129,24 +129,27 @@ and enqueue buffers, when enough buffers are stacked up output is
started. In the write loop, when the application runs out of free
buffers it must wait until an empty buffer can be dequeued and reused.
Two methods exist to suspend execution of the application until one or
more buffers can be dequeued. By default ``VIDIOC_DQBUF`` blocks when no
buffer is in the outgoing queue. When the ``O_NONBLOCK`` flag was given
to the :ref:`open() <func-open>` function, ``VIDIOC_DQBUF`` returns
immediately with an ``EAGAIN`` error code when no buffer is available. The
more buffers can be dequeued. By default :ref:`VIDIOC_DQBUF
<VIDIOC_QBUF>` blocks when no buffer is in the outgoing queue. When the
``O_NONBLOCK`` flag was given to the :ref:`open() <func-open>` function,
:ref:`VIDIOC_DQBUF <VIDIOC_QBUF>` returns immediately with an ``EAGAIN``
error code when no buffer is available. The
:ref:`select() <func-select>` and :ref:`poll() <func-poll>`
functions are always available.
To start and stop capturing or displaying applications call the
:ref:`VIDIOC_STREAMON` and
:ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` and
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` ioctls. Note that
``VIDIOC_STREAMOFF`` removes all buffers from both queues and unlocks
all buffers as a side effect. Since there is no notion of doing anything
"now" on a multitasking system, if an application needs to synchronize
with another event it should examine the struct
:ref:`v4l2_buffer <v4l2-buffer>` ``timestamp`` of captured or
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` removes all buffers from
both queues and unlocks all buffers as a side effect. Since there is no
notion of doing anything "now" on a multitasking system, if an
application needs to synchronize with another event it should examine
the struct :ref:`v4l2_buffer <v4l2-buffer>` ``timestamp`` of captured or
outputted buffers.
Drivers implementing DMABUF importing I/O must support the
``VIDIOC_REQBUFS``, ``VIDIOC_QBUF``, ``VIDIOC_DQBUF``,
``VIDIOC_STREAMON`` and ``VIDIOC_STREAMOFF`` ioctls, and the
:ref:`select() <func-select>` and :ref:`poll() <func-poll>` functions.
:ref:`VIDIOC_REQBUFS <VIDIOC_REQBUFS>`, :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`,
:ref:`VIDIOC_DQBUF <VIDIOC_DQBUF>`, :ref:`VIDIOC_STREAMON
<VIDIOC_STREAMON>` and :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` ioctls,
and the :ref:`select() <func-select>` and :ref:`poll() <func-poll>`
functions.